在运行时拦截子进程的标准输出

2022-01-18 00:00:00 python process subprocess popen stdout

问题描述

如果这是我的子流程:

import time, sys
for i in range(200):
    sys.stdout.write( 'reading %i
'%i )
    time.sleep(.02)

这是控制和修改子进程输出的脚本:

And this is the script controlling and modifying the output of the subprocess:

import subprocess, time, sys

print 'starting'
    
proc = subprocess.Popen(
    'c:/test_apps/testcr.py',
    shell=True,
    stdin=subprocess.PIPE,
    stdout=subprocess.PIPE  )

print 'process created'

while True:
    #next_line = proc.communicate()[0]
    next_line = proc.stdout.readline()
    if next_line == '' and proc.poll() != None:
        break
    sys.stdout.write(next_line)
    sys.stdout.flush()
    
print 'done'

为什么 readline 和 communicate 一直等到进程完成运行?有没有一种简单的方法可以实时传递(和修改)子进程的标准输出?

Why is readline and communicate waiting until the process is done running? Is there a simple way to pass (and modify) the subprocess' stdout real-time?

我使用的是 Windows XP.

I'm on Windows XP.

解决方案

正如 Charles 已经提到的，问题在于缓冲.我在为 SNMPd 编写一些模块时遇到了类似的问题，并通过将 stdout 替换为自动刷新版本来解决它.

As Charles already mentioned, the problem is buffering. I ran in to a similar problem when writing some modules for SNMPd, and solved it by replacing stdout with an auto-flushing version.

我使用了以下代码，灵感来自 ActiveState 上的一些帖子:

I used the following code, inspired by some posts on ActiveState:

class FlushFile(object):
    """Write-only flushing wrapper for file-type objects."""
    def __init__(self, f):
        self.f = f
    def write(self, x):
        self.f.write(x)
        self.f.flush()

# Replace stdout with an automatically flushing version
sys.stdout = FlushFile(sys.__stdout__)

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